Loans Receivable and Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended								7 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) SecurityLoan Contract borrower	Dec. 31, 2014 USD ($) SecurityLoan Contract borrower	Dec. 31, 2013 USD ($)	May. 30, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortization of interest income										$ 1,100,000	$ 694,000	$ 1,286,000
Principal amount of nonaccrual loans	$ 44,400,000				$ 53,900,000				$ 53,900,000	$ 44,400,000	$ 53,900,000
Number of loans 90 days past due and still accruing | Contract										1	0
Recorded Investment 90 days accruing	165,000				0				0	$ 165,000	$ 0
Increase in interest income										1,200,000	$ 1,877,000	1,913,000
Impaired loan defined floor limit (greater than)	1,000,000									$ 1,000,000
Impaired loans number | SecurityLoan										148	147
Impaired loans	50,867,000				85,395,000				85,395,000	$ 50,867,000	$ 85,395,000
Number of troubled debt restructurings | SecurityLoan											143
Number of borrowers | borrower										120	120
Loans and leases receivable, impaired, nonperforming, accrual of interest					81,700,000				81,700,000		$ 81,700,000
Charge-offs										$ 8,828,000	10,872,000	14,406,000
Allowances for loan losses	2,271,000				7,127,000				7,127,000	$ 2,271,000	$ 7,127,000
Weighted average modified interest rate										5.25%	4.58%
Yield percentage rate										5.71%	5.69%
Loans declined									1,800,000	$ 1,100,000
Interest income	74,349,000	$ 73,013,000	$ 72,188,000	$ 72,231,000	73,800,000	$ 73,652,000	$ 67,386,000	$ 64,523,000		291,781,000	$ 279,361,000	$ 252,777,000
Average balances of impaired loans										51,225,000	87,869,000
Loan commitments	866,403,000				908,581,000				908,581,000	866,403,000	908,581,000
Undisbursed home equity and personal credit lines	287,942,000				300,029,000				300,029,000	287,942,000	300,029,000
No Allowance For Loan Losses Required [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired financing receivable with no related allowance	33,376,000				18,346,000				18,346,000	33,376,000	18,346,000
With Related Allowance For Loan Losses [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses	2,271,000				7,127,000				7,127,000	$ 2,271,000	$ 7,127,000
Impaired Loans Troubled Debt Restructurings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans number | SecurityLoan										143
Impaired loans	43,900,000									$ 43,900,000
Number of troubled debt restructurings | SecurityLoan										122	123
Loans and leases receivable, impaired, nonperforming, accrual of interest	26,000,000				54,800,000				54,800,000	$ 26,000,000	$ 54,800,000
Charge-offs										465,000
Allowances for loan losses	99,000				419,000				419,000	$ 99,000	$ 419,000
Residential Commercial And Commercial Mortgage Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans number | SecurityLoan										148	147
Impaired loans	50,900,000				85,400,000				85,400,000	$ 50,900,000	$ 85,400,000
Residential Commercial And Commercial Mortgage Loan [Member] | Non Accrual [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans number | SecurityLoan										26	24
Impaired loans	24,894,000				30,619,000				30,619,000	$ 24,894,000	$ 30,619,000
Team Capital [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of acquired loans													$ 5,220,000
Certain loans acquired in transfer not accounted for as debt securities	$ 3,400,000				$ 4,500,000				$ 4,500,000	3,400,000	4,500,000		$ 5,200,000
Interest income										$ 230,000	$ 348,000